assertions_on_constants incorrectly lints indirect usage of `cfg!`

[Techcable]

Lint name: assertions_on_constants

I tried this code:

const CFG_FLAG: bool = cfg!(config_thing);

fn main() {
    assert!(!CFG_FLAG); // This gives a warning
    assert!(!cfg!(config_thing)); // But direct usage of cfg! is suppressed
}

Indirect usage of cfg!() flags should not give a warning, just like direct usage.

Meta

• cargo clippy -V: clippy 0.1.56 (0fa3190 2021-08-12)
• rustc -Vv:

rustc 1.56.0-nightly (0fa319039 2021-08-12)
binary: rustc
commit-hash: 0fa3190394475a84360b34e074e719d519bc40f1
commit-date: 2021-08-12
host: x86_64-unknown-linux-gnu
release: 1.56.0-nightly
LLVM version: 12.0.1

This false positive also happens on the latest stable as well...

Thanks for your time!

[1nF0rmed]

If I understand correctly, we want to check variables that are set to a cfg! macro return value.
Which when passed to assert!, the lint should suppress the warning messages for such cases.

What's the part of code I'll be looking at for this, and are there tests around this?

[1nF0rmed]

If I'm not wrong, then this is the section/file where the change is to be made

rust-clippy/clippy_lints/src/assertions_on_constants.rs

Lines 85 to 99 in 9205e3d

	} else if let Some(assert_span) = is_direct_expn_of(e.span, "assert") {
	if assert_span.from_expansion() {
	return;
	}
	if let Some(assert_match) = match_assert_with_message(cx, e) {
	match assert_match {
	// matched assert but not message
	AssertKind::WithoutMessage(false) => lint_false_without_message(),
	AssertKind::WithoutMessage(true) | AssertKind::WithMessage(_, true) => lint_true(false),
	AssertKind::WithMessage(panic_message, false) => lint_false_with_message(panic_message),
	};
	}
	}
	}
	}

We would have to check if the grandchild of the current span(e.span) is of Macro (bang) type and has the name "cfg", if the condition matches then we just return.
Would this be the right approach?

[giraffate]

Oh, this seems to be what was intended: #7319

[1nF0rmed]

@giraffate If I'm not wrong #7319 only handles the checks when cfg!(..) was given directly in an assert. The current issue is working with variables that have the value set from cfg!(..).

[pitaj]

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